1. Field of the Invention
This invention relates to image reproduction systems that employ photohardenable image forming layers which are exposed with actinic radiation or heat and dusted with pigments or dyes. More particularly, this invention relates to the use of an additional layer of photohardenable material coated thereon as a protective top coat.
2. Description of the Prior Art
The prior art describes many photopolymerizable elements, hardenable by actinic radiation, which are useful in the printing and proofing industry, for example. In many instances, after the final image bearing product is made, an additional layer of photohardenable material is laminated thereon and hardened by further over-all exposure to actinic light to form a clear, tough protective top coat over the image bearing element. A particularly useful application of this embodiment is taught by Chu and Cohen in U.S. Pat. No. 3,649,268, Mar. 14, 1972. This element is used in the color proofing industry, for example. A layer of photopolymerizable material is laminated to a support, exposed through a particular color positive to actinic radiation to selectively raise the stick temperature of those areas receiving the radiation, and the resulting image "toned" by dusting with a toner of the desired color. By repeating the lamination, exposure and toning step a four color copy of the original is achieved. A final layer of photopolymer is usually applied to the finished product, given an over-all exposure to actinic radiation to harden said layer and serve as a protective shield for subsequent handling of the finished piece. The element so produced will have a glossy appearance which is sometimes objectionable since these elements are used to prepare proofs of material for the printing industry and the printed page is not always glossy in nature. Thus, the user often desires to have a matte-like finish so that his proof most closely resembles that which is to be achieved in the final printing step. This matte finish has been difficult to achieve, particularly in the color proofing industry where, for example, the elements and processes of Chu and Cohen U.S. Pat. No. 3,649,268 are most frequently employed. One such method involves the spraying of the final image layer with a commonly used delustering agent such as "Blair Spray Dull", Blair Arts Products, Inc., Memphis, Tenn. The use of spraying agents is messy and usually involves hazardous, flammable sprays which are inconvenient and noxious. Some sprays do not often cover the layer properly and yield a poor matte finish.
Another method of achieving a matte finish is to incorporate a particulate matter in the super coat as has been well taught in the prior art. However, the conventional top coat used by the color proofing industry is a layer of unexposed photohardenable material laminated over the final image as previously described. If this particulate matter is first incorporated within the material used to prepare the top-coat it is necessary to expose the photopolymer contained therein since in its unpolymerized state it is soft and tacky and cannot be conveniently handled. Also, this step would require that a separate unit of photopolymer containing the delustering agent be maintained for this special use which would be expensive. On the other hand, if the delustering agent is applied to the tacky top-coat and subsequently exposed by the conventional methods, i.e. in a vacuum frame, the particulate matter laid down is forced into the image area causing deformation. This too is highly objectionable and cannot be tolerated.